Control of Intensity of Deformation in Puerto Rico by Mobile Serpentinized Peridotite Basement

Abstract

Puerto Rico is part of a geanticlinal ridge on the ocean floor, built by deposition of sedimentary and volcanic rocks in and around a volcanic framework. Shallow-water sediments and volcanic rocks formed rock sequences on this ridge during the Late Cretaceous and early Tertiary.

Lithology, field relationships, and structure of the Pounamu Ultramafics from the Whitcombe and Hokitika Rivers, Westland, New Zealand

“…3), and in the hinge zone of folds serpentinite is much thicker than on the limbs. Although this thickening may be attributed in part to the similar style of the folds themselves, the presence of mob ilised serpentinite in the cores of isoclinal folds has been widely reported elsewhere (e.g., Milovanovic & Karamata 1960;Knipper 1965;Suzuki 1965Suzuki , 1967Suzuki , 1972Mattson & Schwartz 1971) and has been attributed to diapiric movement. Locally in the hinge zones of several folds from the Whitcombe area, the overlying metabasite cover has been pierced to juxtapose serpentinite with quartzofeldspathic schist (e.g., Tom Creek, see Fig.…”

Cretaceous-Paleogene thrust emplacement of serpentinite in southwestern Puerto Rico

“…Our bastite foliation measurements in the Monte del Estado and Río Guanajibo belts mostly strike N-S and dip to the east (Fig. 4C), in disagreement with the circular pattern generated by Mattson and Schwartz (1971) from measurements in Punta Guanajibo.…”

“…Mattson (1960) attributed diapirism to contraction that mobilized the serpentinite and caused upward movement into the cores of anticlines. This hypothesis was based on local steeply dipping pyroxene foliations in the Río Guanajibo serpentinite (Mattson, 1964;Schwartz, 1970;Mattson and Schwartz, 1971), vertical contacts with Late Cretaceous rocks (Mattson, 1960), and inclusions of Late Cretaceous mudstone and volcanic rocks within the serpentinite (Mattson, 1960). Curet (1986) also supported emplacement by diapirism.…”

“…The hypothesis of serpentinite diapirism in southwestern Puerto Rico is based on reports of steeply dipping pyroxene foliation and the circular pattern of poles to bastite foliation on a stereonet (Mattson, 1964;Schwartz, 1970;Mattson and Schwartz, 1971). However, pyroxene deforms plastically at temperatures higher (>800 °C; Ross et al, 1980;Nicolas, 1989) than the upper temperature boundary of serpentinization (550 °C;O'Hanley, 1996).…”